Dear Tom and Ray: My boyfriend insists on revving the engine when he’s performing a jump-start. He revs the good car when he starts it up, and then revs the bad car when he starts it up. Is there any reason for doing this? Is there anytime when it is good or when you need to rev your engine? Thanks.
– Amanda
Ray: Bad news, Amanda. Your boyfriend is more or less right. I know that’s not the news you were hoping to hear.
Tom: Revving up the engine during a jump-start is not a bad idea, within reason. You never want to “floor” the gas pedal, under any circumstances. But when your engine turns faster, the engine’s alternator also turns faster. And when an alternator turns faster, it produces more electricity.
Ray: So by revving your engine up to 2,000 rpm or 2,500 rpm and holding it there while the other car tries to start, you’re increasing the output of your alternator and giving your battery a little bit of extra power, which it can donate to the other car. Depending on the respective engine sizes and battery conditions, that extra power could make a difference.
Tom: It’s also smart to make sure that when you jump-start another car, all of your electrical accessories are turned off. The less electricity you’re demanding for your own car, the more you can donate. So you want to turn off the headlights, the air conditioner and subwoofer, and the electric butt-scratcher.
Ray: For the car that’s receiving the jump-start the same rules apply. You want to turn all of the accessories off.
That way, all of the alternator’s power can be directed to recharging the battery. Once the car starts, you CAN rev it up to charge the battery faster, but the best way to do that is to just drive it. If you just left the dome light on, 20 minutes or half an hour of driving should be enough. But if you left the headlights and the Easy Bake Oven on all night, it might take a lot longer for the battery to fully charge again.
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Dear Tom and Ray: I recently saw a car catalog that had an oil-filter magnet for sale. The magnet was placed on the bottom of an oil filter and was strong enough to remove any metal shavings from the oil stream. Is this product worthwhile, or am I just wasting my money?
– Ron
Tom: These things have been around for years, Ron. They certainly don’t do any harm.
Ray: They sell magnets that go inside the oil pan, magnets that are built into the oil plug, and magnets, like this one, that attach to the filter.
Tom: Now, keep in mind that the oil filter itself already removes any metal shavings, or anything else that’s bigger than about 25 microns – or about half the width of a human hair. So they do a pretty good job. But If a magnet really made engines last longer, don’t you think that GM and Ford would already have spent the three cents per car it would take to build one into the oil plug?
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